I am supposed to be able to pull a 9 shank with my 140hp tractor. I found and bought a 7 shank Glencoe SS, and glad I did. I have very tough yellow clay soil.
That is 20 hp per shank, and I pulled through dry compacted soil the plow would not stay in last year. Basically think a paved parking lot..... Very tough conditions within the tough soil I have.
So I think you have a good shot at the 5 shank working out for you.